1. Field of the Invention
This invention relates to a displacement detecting apparatus incorporating therein a detector for detecting a relative moving displacement between a main body and a measuring element, and more particularly to improvements in a displacement detecting apparatus constructed such that assembling and adjustment of the detector can be facilitated.
2. Description of the Prior Art
For example, in contrast to a mechanical dial gauge wherein a spindle provided at the forward end portion thereof with a measuring element is slidably supported by a case body, an axial moving displacement of the spindle is converted into a rotary angle of a pointer through a mechanically enlarging mechanism, and a measured value is read in cooperation between this pointer and graduations, there has been known a displacement detecting apparatus, a so-called electronic dial gauge, wherein a moving displacement thereof is transduced into an electric signal by a detector incorporated therein, and the electric signal is electronically indicated in display means such as a digital and/or analog indicator. The latter has been widely spread due to its characteristics of high accuracy and easiness in reading.
The detectors of the displacement detecting apparatus of the type described are selected from the systems including a electrostatic capacity system, photoelectric system, magnetic system, contact point system and the like in accordance with the requisites such as the purpose of use, required measuring accuracy and further power consumption. However, any one of the systems has been constructed such that a first and a second sensing members are provided on a movable member such as the spindle and on a fixed member such as the case body in a manner to be movable relative to each other, respectively. Here, the first and second sensing members, being varied in shape due to the principle, system and the like, may be a pair of electrode plates opposed to each other, a main scale and an index scale having optical lattices associated with each other, a magnetic scale and a magnetic head, or an electrode plate and an electric contact. However, on condition that the positional relationship therebetween is regularly supported, the detector has been able to attain a resolution as high as an order of scores of - 10 .mu.m.
However, with the conventional detector as described above, such a problem has been presented that assembling and adjusting of the positional relationship between the both sensing members are very difficult to do. This problem will hereunder be described in conjunction with an example of the detector 100 of a phase discrimination type electrostatic capacity system as shown in FIGS. 5 and 6. More specifically, as shown in FIG. 5, a plurality of sending electrodes 32 are arranged at regular intervals and in a predetermined pattern on the outer surface of a stationary plate 31 consisting of a stator or scale plate fixed to the side of a main body of apparatus such as a case body, and further, a belt-shaped receiving electrode 33 is provided in parallel to these sending electrodes 32. The respective sending electrodes 32 are applied thereto with AC voltage signals different in phase from one another.
A movable plate 41 consisting of a rotor or movable scale plate interlocked with a movable member such as a spindle is opposed to the stationary plate 31. On this movable plate 41, there are alternately provided along the moving direction of the movable plate 41 a coupling electrode 42 opposed to the sending electrodes 32 and the receiving electrode 33, and overlying both of the electrodes, and an earth electrode 43 opposed to the sending electrodes 32 and the receiving electrode 33, and also overlying both of the electrodes.
On the other hand, voltage signals associated with voltage signals of the respective sending electrodes 32 are induced to the receiving electrode 33 through the coupling electrodes 42, and accordingly, when the movable member is displaced in the state where AC voltages different in phase from one another are applied to the respective sending electrodes 32, an output signal commensurate to a displacement value of the movable member can be obtained from the receiving electrode 33. The phase of the signal outputted from the receiving electrode 33 is processed in an integrator 36 and compared with a predetermined reference phase, so that the displacement value of the movable member can be accurately measured without being affected by fluctuations and the like of a power voltage.
In the detector 100 constructed as described above, distances between the sending electrodes 32, the receiving electrode 33 and the coupling electrode 42 are important from the viewpoint of accuracy and should be held in the order of scores of .mu.m, and the parallelism therebetween should not be fluctuated as well. Further, even if there may be a relative movement between the stationary plate 31 and the movable plate 41, the distances between the electrodes and the parallelism should be maintained. Moreover, for example, even if the parallelism between the both plates 31 and 41 is maintained, fluctuations in an area ratio of electrodes due to the inclinations and shifts in positions, etc. of the both plates 31 and 41 are not allowed. If these positional relationships are brought into disorder, then fluctuations in S/N ratio occur, and not only a predetermined detecting accuracy cannot be secured but also impossibility of detecting due to contact and the like between both plates 31 and 41 occurs. Here, in the recent years, during which necessity has been voiced for compactness of the displacement detecting apparatus in order to improve the portability and controllability. To assemble the displacement detecting apparatus with the aforesaid positional relationship is very troublesome in particular, and, by use of a method of monitoring output voltages and the like and disassembling the displacement detecting apparatus again for adjusting, while actual operations are carried out after the assembling, it is particularly difficult to obtain a resolution of less then 1 .mu.m. This problem is true of not only the case of the detector of the electrostatic capacity system but also the case of the detectors of the above-described photoelectric system and the like.
Now, the following problem has been presented when the detector 100 of the aforesaid phase discriminating type electrostatic capacity system is provided on a displacement detecting apparatus such as the electronic dial gauge.
More specifically, when the detector 100 is adapted to well-known slide calipers, height gauge and the like, e.g. electronic slide calipers as shown in FIG. 7, the stationary plate 31 having the sending electrodes 32 and the receiving electrode 33 is secured to a slider 70 integrally formed thereon with an electronic display means 21, a movable plate 41 having a coupling electrode 42 and earth electrode 43 is mounted to a main scale 71, winding is made such that, in the slider 70, AC voltages are applied to the sending electrodes 32 and an output signal can be led out of the receiving electrode 33, and the earth electrode 43 is conductively wired to the main scale 71, so that a predetermined operation can be performed. However, since the movable plate 41 is projected in the diametral direction of the spindle in the case of the displacement detecting apparatus such as the electronic dial gauge, the earth electrode 43 and the spindle should have been wired by use of a cable surrounding the movable plate 41. As a consequence, in order to secure a sufficient space to allow the cable not to interface with any other assembly, the displacement detecting apparatus as a whole should have been large-sized. Furthermore, such a problem has been presented that a connecting terminal portion of the cable is dislodged due to the frequent vertical motions of the spindle. Further, due to the presence of the above-described problems, an ultra compact type displacement detecting apparatus, regardless of the above-described characteristics thereof, cannot adapt the detector of the phase discriminating type electrostatic capacity system from the restriction of the construction thereof, thus causing the hindrance against wide spreading of the displacement detecting apparatus with high accuracy.